[clangd] Make use of diagnostic tags for some clang diags

It is not great to list diag ids by hand, but I don't see any other
solution unless diagnostics are annotated with these explicitly, which is a
bigger change in clang and I am not sure if would be worth it.

Diagnostics handled by this patch is by no means exhaustive, there might be
other checks that don't mention "unused"/"deprecated" in their names. But it
feels like this should be enough to catch common diagnostics and can be extended
over time.

Differential Revision: https://reviews.llvm.org/D107040

clang-tools-extra/clangd/Diagnostics.cpp

@@ -26,6 +26,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/ScopeExit.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/Capacity.h"
@@ -35,6 +36,7 @@
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <cstddef>
+#include <vector>
 
 namespace clang {
 namespace clangd {
@@ -324,6 +326,60 @@ std::string noteMessage(const Diag &Main, const DiagBase &Note,
   OS.flush();
   return capitalize(std::move(Result));
 }
+
+void setTags(clangd::Diag &D) {
+  static const auto *DeprecatedDiags = new llvm::DenseSet<unsigned>{
+      diag::warn_access_decl_deprecated,
+      diag::warn_atl_uuid_deprecated,
+      diag::warn_deprecated,
+      diag::warn_deprecated_altivec_src_compat,
+      diag::warn_deprecated_comma_subscript,
+      diag::warn_deprecated_compound_assign_volatile,
+      diag::warn_deprecated_copy,
+      diag::warn_deprecated_copy_with_dtor,
+      diag::warn_deprecated_copy_with_user_provided_copy,
+      diag::warn_deprecated_copy_with_user_provided_dtor,
+      diag::warn_deprecated_def,
+      diag::warn_deprecated_increment_decrement_volatile,
+      diag::warn_deprecated_message,
+      diag::warn_deprecated_redundant_constexpr_static_def,
+      diag::warn_deprecated_register,
+      diag::warn_deprecated_simple_assign_volatile,
+      diag::warn_deprecated_string_literal_conversion,
+      diag::warn_deprecated_this_capture,
+      diag::warn_deprecated_volatile_param,
+      diag::warn_deprecated_volatile_return,
+      diag::warn_deprecated_volatile_structured_binding,
+      diag::warn_opencl_attr_deprecated_ignored,
+      diag::warn_property_method_deprecated,
+      diag::warn_vector_mode_deprecated,
+  };
+  static const auto *UnusedDiags = new llvm::DenseSet<unsigned>{
+      diag::warn_opencl_attr_deprecated_ignored,
+      diag::warn_pragma_attribute_unused,
+      diag::warn_unused_but_set_parameter,
+      diag::warn_unused_but_set_variable,
+      diag::warn_unused_comparison,
+      diag::warn_unused_const_variable,
+      diag::warn_unused_exception_param,
+      diag::warn_unused_function,
+      diag::warn_unused_label,
+      diag::warn_unused_lambda_capture,
+      diag::warn_unused_local_typedef,
+      diag::warn_unused_member_function,
+      diag::warn_unused_parameter,
+      diag::warn_unused_private_field,
+      diag::warn_unused_property_backing_ivar,
+      diag::warn_unused_template,
+      diag::warn_unused_variable,
+  };
+  if (DeprecatedDiags->contains(D.ID)) {
+    D.Tags.push_back(DiagnosticTag::Deprecated);
+  } else if (UnusedDiags->contains(D.ID)) {
+    D.Tags.push_back(DiagnosticTag::Unnecessary);
+  }
+  // FIXME: Set tags for tidy-based diagnostics too.
+}
 } // namespace
 
 llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, const DiagBase &D) {
@@ -461,6 +517,7 @@ void toLSPDiags(
       Main.relatedInformation->push_back(std::move(RelInfo));
     }
   }
+  Main.tags = D.Tags;
   OutFn(std::move(Main), D.Fixes);
 
   // If we didn't emit the notes as relatedLocations, emit separate diagnostics
@@ -504,6 +561,7 @@ std::vector<Diag> StoreDiags::take(const clang::tidy::ClangTidyContext *Tidy) {
 
   // Fill in name/source now that we have all the context needed to map them.
   for (auto &Diag : Output) {
+    setTags(Diag);
     if (const char *ClangDiag = getDiagnosticCode(Diag.ID)) {
       // Warnings controlled by -Wfoo are better recognized by that name.
       StringRef Warning = DiagnosticIDs::getWarningOptionForDiag(Diag.ID);

clang-tools-extra/clangd/Diagnostics.h

@@ -19,6 +19,7 @@
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringSet.h"
 #include "llvm/Support/JSON.h"
 #include "llvm/Support/SourceMgr.h"
@@ -106,6 +107,7 @@ struct Diag : DiagBase {
   std::vector<Note> Notes;
   /// *Alternative* fixes for this diagnostic, one should be chosen.
   std::vector<Fix> Fixes;
+  llvm::SmallVector<DiagnosticTag, 1> Tags;
 };
 llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, const Diag &D);
 

clang-tools-extra/clangd/Protocol.cpp

@@ -584,6 +584,8 @@ llvm::json::Value toJSON(const DiagnosticRelatedInformation &DRI) {
   };
 }
 
+llvm::json::Value toJSON(DiagnosticTag Tag) { return static_cast<int>(Tag); }
+
 llvm::json::Value toJSON(const Diagnostic &D) {
   llvm::json::Object Diag{
       {"range", D.range},
@@ -602,6 +604,8 @@ llvm::json::Value toJSON(const Diagnostic &D) {
     Diag["relatedInformation"] = *D.relatedInformation;
   if (!D.data.empty())
     Diag["data"] = llvm::json::Object(D.data);
+  if (!D.tags.empty())
+    Diag["tags"] = llvm::json::Array{D.tags};
   // FIXME: workaround for older gcc/clang
   return std::move(Diag);
 }

clang-tools-extra/clangd/Protocol.h

@@ -28,6 +28,7 @@
 #include "support/MemoryTree.h"
 #include "clang/Index/IndexSymbol.h"
 #include "llvm/ADT/Optional.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/JSON.h"
 #include "llvm/Support/raw_ostream.h"
 #include <bitset>
@@ -811,6 +812,19 @@ struct DiagnosticRelatedInformation {
 };
 llvm::json::Value toJSON(const DiagnosticRelatedInformation &);
 
+enum DiagnosticTag {
+  /// Unused or unnecessary code.
+  ///
+  /// Clients are allowed to render diagnostics with this tag faded out instead
+  /// of having an error squiggle.
+  Unnecessary = 1,
+  /// Deprecated or obsolete code.
+  ///
+  /// Clients are allowed to rendered diagnostics with this tag strike through.
+  Deprecated = 2,
+};
+llvm::json::Value toJSON(DiagnosticTag Tag);
+
 struct CodeAction;
 struct Diagnostic {
   /// The range at which the message applies.
@@ -830,6 +844,9 @@ struct Diagnostic {
   /// The diagnostic's message.
   std::string message;
 
+  /// Additional metadata about the diagnostic.
+  llvm::SmallVector<DiagnosticTag, 1> tags;
+
   /// An array of related diagnostic information, e.g. when symbol-names within
   /// a scope collide all definitions can be marked via this property.
   llvm::Optional<std::vector<DiagnosticRelatedInformation>> relatedInformation;

clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp

@@ -65,6 +65,11 @@ WithNote(::testing::Matcher<Note> NoteMatcher1,
   return Field(&Diag::Notes, UnorderedElementsAre(NoteMatcher1, NoteMatcher2));
 }
 
+::testing::Matcher<const Diag &>
+WithTag(::testing::Matcher<DiagnosticTag> TagMatcher) {
+  return Field(&Diag::Tags, Contains(TagMatcher));
+}
+
 MATCHER_P2(Diag, Range, Message,
            "Diag at " + llvm::to_string(Range) + " = [" + Message + "]") {
   return arg.Range == Range && arg.Message == Message;
@@ -665,6 +670,7 @@ TEST(DiagnosticsTest, ToLSP) {
 
   clangd::Diag D;
   D.ID = clang::diag::err_undeclared_var_use;
+  D.Tags = {DiagnosticTag::Unnecessary};
   D.Name = "undeclared_var_use";
   D.Source = clangd::Diag::Clang;
   D.Message = "something terrible happened";
@@ -710,6 +716,7 @@ main.cpp:6:7: remark: declared somewhere in the main file
 
 ../foo/baz/header.h:10:11:
 note: declared somewhere in the header file)";
+  MainLSP.tags = {DiagnosticTag::Unnecessary};
 
   clangd::Diagnostic NoteInMainLSP;
   NoteInMainLSP.range = NoteInMain.Range;
@@ -1419,6 +1426,24 @@ TEST(Preamble, EndsOnNonEmptyLine) {
         testing::Contains(Diag(Code.range(), "no newline at end of file")));
   }
 }
+
+TEST(Diagnostics, Tags) {
+  TestTU TU;
+  TU.ExtraArgs = {"-Wunused", "-Wdeprecated"};
+  Annotations Test(R"cpp(
+  void bar() __attribute__((deprecated));
+  void foo() {
+    int $unused[[x]];
+    $deprecated[[bar]]();
+  })cpp");
+  TU.Code = Test.code().str();
+  EXPECT_THAT(*TU.build().getDiagnostics(),
+              UnorderedElementsAre(
+                  AllOf(Diag(Test.range("unused"), "unused variable 'x'"),
+                        WithTag(DiagnosticTag::Unnecessary)),
+                  AllOf(Diag(Test.range("deprecated"), "'bar' is deprecated"),
+                        WithTag(DiagnosticTag::Deprecated))));
+}
 } // namespace
 } // namespace clangd
 } // namespace clang